chore(repo): DX cleanup — categorise examples, text-diffable golden, build/ output (#27 #28 #30)

Repository-cleanup / DX pass folding three tracker items into one coherent
change, verified green end to end (`bin/x test` 49/0, `bin/x selfhost-test`
29/0, `bin/x test-tools` 29/0).

#28 — curate & categorise examples/
- 42 flat entries regrouped into intent-revealing subdirs: games/, rendering/,
  ecs/, events/, networking/, lang/, library/ (was lib/).
- chronorift dir-vs-file duplication resolved: the entry file and its import
  modules now live together under games/chronorift(.ludic).
- Every path reference updated repo-wide (test runner, editor-tool drivers,
  docs/site, design docs).
- New examples/README.md indexes the whole set with run commands.
- Showcase examples without a self-asserting entry (hello, events, net_rt) now
  get a compile-only rot guard in `bin/x test`, so nothing here rots silently.

#30 — text-diffable golden baseline
- The 4 binary selfhost/golden/*.ppm blobs are replaced by a single
  selfhost/golden/renders.sha256 manifest (SHA-256 per render). Hashes are
  byte-identical to the old PPMs, so the baseline is unchanged — only its form.
- game_case now compares framebuffer hashes; a regression shows as a changed
  hex line in review, not "binary files differ".
- New `bin/x golden` regenerates the manifest deliberately (review with
  `git diff selfhost/golden/renders.sha256`).

#27 — PPM & asset handling
- Headless renders now write build/out.ppm, never the repo root; `x app`,
  `x clean`, messaging and .gitignore updated to match. Nothing is written to
  the working root any more.
- Redundant local Kenney .zip archives removed (the art ships extracted;
  .gitignore already excludes *.zip). CC0 License.txt files retained.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/reason.ludic

@@ -1,38 +0,0 @@
-# reason.ludic — LC1 reason-carrying teardown. One @OnDespawn hook, but it knows
-# *why* the entity is ending: `reason: r` binds an EndReason the compiler passes
-# at each teardown site. An in-world `despawn` passes EndReason.Despawned; program
-# shutdown passes EndReason.Quit (every still-live entity's hook fires at exit — no
-# silent deaths). The body branches on the reason, exactly as Unreal's
-# EndPlay(reason) / Erlang's terminate(Reason) do.
-#
-# Running it prints: 503 1009
-#   503    Enemy A despawned in-world (Despawned): drop its loot, 3 + 500
-#   1009   Enemy B outlived the run; at quit (Quit) it skips loot, 9 + 1000
-#
-#   bin/x game-build bin/ludicc examples/reason.ludic /tmp/reason
-#   /tmp/reason </dev/null
-program Reasons {
-  property Health { hp: int = 0 }
-  property Loot   { gold: int = 0 }
-  model Enemy { Health, Loot }
-
-  @OnDespawn(Enemy, reason: r) handler Clean {
-    match r {
-      EndReason.Quit => { print(Health.hp + 1000) }   # app closing — don't bother dropping loot
-      _              => { print(Loot.gold + 500) }     # died in-world — drop the loot
-    }
-  }
-
-  handler Seed phase Start {
-    spawn Enemy { Health { hp: 7 }, Loot { gold: 3 } }   # A
-    spawn Enemy { Health { hp: 9 }, Loot { gold: 4 } }   # B
-  }
-
-  handler Run phase Render {
-    var first = 0
-    for (e) in query [Health] {
-      if first == 0 { despawn self(); first = 1 }        # despawn A -> Despawned -> 3 + 500 = 503
-    }
-    quit()                                               # B survives -> Quit -> 9 + 1000 = 1009
-  }
-}